This invention relates to a dual image viewer.
Infrared viewers, such as the Probeye (trade mark) infrared viewer produced by the Hughes Aircraft Company, are used for many purposes in survey work. For example, when used in an aircraft, these devices, which are sensitive to the emission of infrared radiation, can detect underground forest fires which are visually undetectable. These viewers convert the infrared image to an image within the visual spectrum. This visual image can be viewed by the eye or reproduced on photographic film if a camera is positioned on the eyepiece.
In many situations, it is desirable to compare the infrared image of a scene with the normal visual image. For example, when detecting underground forest fires, it may not be possible to locate the exact position of the fire by means of the infrared image alone. This image may not have a sufficient number of identifiable landmarks to locate the fire. However, if the normal visual image can be viewed adjacent the infrared image, or viewed coincident with the infrared image, all of the surrounding details are added and the particular stump where the fire is burning may be found. Of course, this is only one example of where it would be useful to view the visual and infrared images together and many analogous uses exist.
In the prior art, U.S. Pat. No. 3,730,985 to Whitney discloses an infrared viewer including an optical viewing system and an infrared scanning and display system disposed within a single housing. The visual image enters the unit through a red filter and the infrared image is converted to a blue image by a second viewing system. The red light of the visual image passes through a dichroic element positioned at an angle of 45.degree. to the path of the image, while the blue light from the infrared image is deflected by the dichroic element along the path of the visual image. Consequently, the operator views a blue image superimposed on a red image.
U.S. Pat. No. 4,027,159 to Bishop describes a night vision system combining a reflected-light imaging device with an audio-monitored, far infrared detection device.
U.S. Pat. No. 3,076,961 to Bibbero shows an apparatus for co-ordinating information derived from two or more sensors, such as television and infrared devices.
Infrared viewers are disclosed in such U.S. Pat. Nos. as 3,812,357 to Flogaus, which shows a miniature infrared short range thermal imager, and 3,752,983 to Yanez which deals with an infrared attachment for a single lens reflex camera.
The prior art listed above does not disclose a simple compact dual image viewer for mounting on an infrared scanner so that a visual image, converted from an infrared image by the scanner, is produced coincident with or adjacent a normal visual image.